1. Field of the Invention
The present invention relates to a composite-type electromagnet structured by a combination of an electromagnet having a control coil wound on an electromagnet core and a radial permanent magnet, and to a radial magnetic bearing provided with this composite-type electromagnet.
2. Description of the Related Art
Radial magnetic bearings, which are used for rotatably supporting a rotary shaft of a rotary apparatus such as a motor without making contact therewith, are structured by position sensors, controlling electromagnets and biasing electromagnets. However, there are proposals for employing an electromagnet for both controlling and biasing in order to simplify the structure. The position sensor is used to detect displacement of the rotary shaft in the radial direction and provides a detection signal to a magnetic bearing control device. The biasing electromagnet provides a biasing magnetic flux of a constant magnitude to the rotary shaft through a gap between the rotary shaft and the radial magnetic bearing. The controlling electromagnet serves to apply, in accordance with an output signal from the magnetic bearing control device, a controlling magnetic flux to the rotary shaft via the gap and return the displaced rotary shaft to a predetermined position and hold it in that position.
Because the biasing magnetic field is constant, if it is supplied by a permanent magnet, the biasing electromagnet is unnecessary. If this is done, the lack of need of a biasing current to be flown to an excitation coil of the biasing electromagnet greatly reduces power consumption and heat generation of the radial magnetic bearing. Furthermore, because the number of cores and coils for the biasing electromagnet are reduced, the apparatus size and cost can be reduced. Because these various merits are available, proposal and development are being made for the radial magnetic bearings adopting a composite-type electromagnet combined with a biasing permanent magnet and a controlling electromagnet.
The radial magnetic bearing conventionally disclosed has, as shown in FIG. 10, a plurality of biasing-magnetic-field permanent magnets 54a, 54b, 54c, 54d arranged equidistant at inner positions in a widthwise center of an annular yoke 57. These permanent magnets are clamped between an inner surface of the annular yoke 57 and back surfaces of inner magnetic poles 52a, 52b, 52c, 52d. Each inner magnetic pole has an excitation coil 53a, 53b, 53c, 53d provided on a periphery of a leg thereof. Further, a pair of disc-formed outer magnetic poles 55, 56 defining a plurality of magnetic poles are provided on respective sides of the annular yoke 57 so that the inner magnetic poles and the outer magnetic poles can form a magnetic circuit. Thus, the radial magnetic bearing conventionally disclosed is characterized in that an attracting force of the biasing permanent magnet can be adjusted by varying the thickness of the backside of the inner magnetic pole and a gap between a backside side position and the outer magnetic pole.
Meanwhile, another radial magnetic bearing is a radial magnetic bearing low in current consumption structured as shown FIG. 11. That is, a housing 67 has electromagnet cores 62a, 62b, 62c, 62d in a squared-U form circumferentially arranged around a rotary shaft 69. These electromagnet cores are wound around with excitation coils 63a, 63b, 63c, 63d, and biasing permanent magnets 64a, 64b, 64c, 64d arranged in one-part section thereof. Also, the rotary shaft 69 has a rotor core 66 as a circumferential laminate with an I-type electromagnetic steel plate disposed facing the electromagnet cores 62a, 62b, 62c, 62d. Based on a position sensor signal for detecting a radial position of the rotary shaft 69, a magnetic bearing control device not shown supplies a control current to the excitation coils 63a, 63b, 63c, 63d, thereby controlling a radial position of the rotary shaft 69.
Furthermore, another radial magnetic bearing is a magnetic bearing having, as shown in FIG. 12, a stator arranged around a rotary shaft 79 to apply magnetism to the rotary shaft 79 from the stator to hold the rotary shaft 79 constant on the axis, thus being simple in structure and usable for a large-sized bearing. That is, the stator is structured by electromagnet cores 72a, 72b, 72c, 72d extending along an axial direction and arranged circumferentially, control coils 73a, 73b, 73c, 73d wound around the electromagnet cores, a pair of disc-formed stator yokes 75, 76 respectively fixed on the ends of the electromagnetic cores, a biasing permanent magnet 74 that is a cylindrical permanent magnet connecting between inner sides of the control coils of the stator yokes and magnetized in the axial direction.
In the meanwhile, although not limited to those as the above for use in radial magnetic bearings, in a composite-type electromagnet combined with a permanent magnet and an electromagnet, a magnetic member forming an electromagnet core and a permanent magnet has a bonded junction, e.g. by an epoxy adhesive or joined by mechanically clamping. In the junction between the permanent magnet and the electromagnetic core thus bonded, there always exists a gap though different in degree due to assembling. Though being dependent upon electromagnet size, forming accuracy, etc., the gap is nearly several hundreds xcexcm, which in some cases is an air gap and in other cases a presence of a non-magnetic material such as adhesive. In both cases, it is a factor for preventing magnetic flux flow. This results in problems such as failing to obtain a desired magnetic force or imbalance in magnetic force or further occurrence of magnetic flux leak to the outside thus causing adverse effects upon external apparatuses.
As concerned with putting into practical use a composite-type electromagnet or a radial magnetic bearing having this composite-type electromagnet, there is a problem with prevention of magnetic flux flow in the junction of a magnetic-material electromagnet core and a permanent magnet, besides a problem with adjustment of a biasing magnetic field.
The problem that the invention is to solve is, in a composite-type electromagnet or a radial magnetic bearing having this composite-type electromagnet comprising an electromagnet having a controlling coil wound around an electromagnet core of a magnetic material and a biasing permanent magnet having a junction between the electromagnet core and the permanent magnet, to minimize the leak of magnetic flux occurring at the junction not to reduce the amount of magnetic flux available and prevent bad effects upon an external member, apparatus or the like due to leak magnetic flux.
In order to solve the above problem, a composite-type electromagnet comprises an electromagnet having a controlling coil wound around an electromagnet core of a magnetic material and a biasing permanent magnet having a junction between the electromagnet core and the permanent magnet, wherein a filling material made of a material having a high permeability and a high saturation magnetic flux density is disposed in the junction.